When
I first encountered the word vacuum cool, I was very intrigued. A lot of
people in the industry, from greenhouse material suppliers, seed suppliers and
even end users were told that vacuum cooling can help increase shelf life of
your fresh produce even up to two weeks. So, I decided to get a bag
of lettuce from the other brand that was labeled with "vacuum cool". To my surprise,
it did not even reach 2 days, it started to show signs of deterioration.
What went wrong ? Well this is the truth about
Vacuum Cool ....

Summer
heat in the Philippines soars to as high as 40 degree Celsius during
mid-day. The crops grown inside the greenhouse and in the open field
absorb much of the field heat. It
is therefore very important for the farm to remove the field heat.

The
process of removing the field heat is what we call pre-cooling. It is the first operation in the cold chain.

Room
Cooling. Product is
simply placed in a cooler, and over time, the product temperature
decreases nearly to the cooler temperature. This process takes a long
time, but requires no other equipment than a cooler.

Forced
Air Cooling. It is very similar to room cooling, except
that the cold air is pulled by an electric fan through the stacked boxes
of vegetables. Because of the increased air flow, the cooling rate is much
faster than with room cooling, so that heat is taken from the vegetables
in a very short time. Cooling with forced-air is also more uniform, so
that vegetables in different boxes cool at much the same rate.

Hydro-cooling.
Cool water is sprayed over the
product, or the product is immersed in cool water.

Icing.
This method is applicable only is used for product that can
withstand direct contact with ice, such as beets and broccoli. The
ice can be finely
crushed, flaked, or in a slurry with water. Packaging used with icing must
also be able to withstand wetting.

Vacuum cooling
. The product is placed in a vacuum, so that the atmospheric pressure
around the product is reduced. This reduces the water vapor pressure
around the product, and when it is lowered below that inside the product,
water evaporates from the product. This in turn lowers the surface
temperature of the product.

After pre-cooling activity, the produce are
then transferred to the intermediate storage area where storage
temperatures should be low as possible to slow product metabolic processes
and discourage pathogen growth, but high enough to avoid freezing or
injuring the product.

So, can salad
greens subject to vacuum cooling improve the quality ?

CONCLUSION

Fact #1. There are several
methods of doing pre-cooling activity. Vacuum cooling is just one of
5 methods discussed. Pre-cooling activity is just one of the several farm activities that will determine the final
quality of the fresh produce.

Fact #2. Fresh
produce that are subject to vacuum cooling
does not assure you of longer shelf life if any of the
following conditions are present:

succeeding cold chain is broken;

the temperature of the intermediate
storage area is outside the optimum level;

fresh produce with physical damage are not
removed; or

oxidizing agent is present in the final
packaging.

Fact #3. The reason why vegetables
are also called fresh produce is because they are meant to be consumed
when they are relatively fresh and not two weeks after harvest.